The present invention relates generally to an electropneumatic brake control systems and more specifically to a variable load electropneumatic braking system.
In rail vehicles, the modification of the brake cylinder pressure as a function of the load is well known. This is true in transit as well as freight systems. To achieve the variable load modification, a pneumatic relay valve is provided between the brake control valve and the brake cylinder to modify the signal as a function of the sensed weight. The weight is sensed by the deflection of the springs on the vehicle either mechanically or pneumatically. Continuous variation of the brake signals by changing the area of a balanced piston or diaphragm is illustrated in U.S. Pat. No. 3,285,674 to Eaton. Another example is a variable lever illustrated in U.S. Pat. No. 4,421,360 to Newton.
In freight trains which include substantially more cars in the consist sometime exceeding 100 and extending for over a mile, the load response element of the braking device is known as an empty/load valve. This is a valve which is a qualitative valve which provides either 100% of the brake signal to the brake cylinder or only a fixed percentage thereof. For lighter cars, it provides the smaller percentage of the value. The type of empty/load valve is represented by the percentage of reduction and generally are known as EL/45, EL/50 or EL/60 representing a 45%, 50% and 60% reduction in brake cylinder pressure. Historically, a car that is 20% loaded considered an empty car. An example is illustrated in U.S. Pat. No. 5,211,450 to Gayfer et al.
These conventional empty/load devices obtain an adequately high loaded braking ratio, that provides satisfactory stopping ability and speed control in heavy cars, without having an empty braking ratio which is too high. Thus, loaded cars brake at a higher brake ratio than do empty cars. The purpose of the empty/load device is to eliminate in-train forces that are caused by braking differently loaded cars with the same brake force. In-train forces are also created by braking cars at different times. Although the ultimate goal of electropneumatic braking is to allow braking in all the cars simultaneously, the rate of brake cylinder pressure buildup and the reaching of the maximum braking pressure for each brake cylinder may still vary across the train creating in-train forces.
In addition to trains having loaded and empty cars, the trains may have mixed equipment. Some may have empty/load equipment and others may not. Some may have pneumatic brake control valves and other have electropneumatic brake control valves. In addition to weight, each of the individual cars may have different brake cylinder areas, lever ratios and because of their equipment or age, different braking deficiencies. All of these will change their braking response to a requested braking signal. With the availability of more information and controls on the individual cars on a freight train, there is a desirability to customize the braking response of the individual cars.
The response of conventional equipment with a 50% empty/load valve at a full load brake cylinder pressure of 64 PSI for 6.5% and a 10% gross rail load brake ratio defined at 50 PSI are illustrated in FIG. 1. As can be seen, the braking ratio varies with the weight of the car. Thus, the stopping distance of the train will change depending upon the weight of the individual cars in the consist, if they will each have a different braking ratio.
Thus, it is an object of the present invention to provide a method of braking which allows more consistent stopping distances among trains.
Another object of the present invention is to provide a method wherein a car can make an independent decision on the amount of braking to be made in response to a desired brake command.
An even further object of the present invention is to provide a braking method which is capable of a uniform braking ratio irrespective of the weight of the car.
A still even further object of the present invention is to provide a method of braking individual cars in the train which monitor changing variables which affect appropriate braking responses.
These and other objects are achieved by controlling brakes of a car having electropneumatic brake valves, by determining the weight of the car and calculating the ratio of brake cylinder pressure to train brake command for the car using the weight of the car. Brake cylinder pressure is then determined using the brake train command and the calculated ratio and the brake cylinder pressure is controlled to the determined brake cylinder pressure. The ratio of the brake cylinder to pressure train brake command is calculated by first calculating a full service brake cylinder pressure for the pneumatic car and preferably using a fixed braking ratio. The calculated ratio is used for brake command signals between a first and second value.
A minimum brake cylinder pressure is used for train brake commands between zero and the first value and a maximum brake cylinder pressure is used for train brake commands greater than the second value. The minimum brake cylinder pressure is a fixed value for all determined weights. The maximum brake cylinder pressure is a fixed percentage of a full service brake cylinder pressure for the train brake commands greater than the second Value. The same valves are used to apply and graduated release brake cylinder pressure over the full range of brake command signals. For direct release, the release pressure is a single ratio pressure over the full range of brake commands. A minimum ratio is selected for weights below a minimum weight. If weight cannot be determined, the determined weight is considered to be a fully loaded weight.
The rate of change of brake cylinder pressure is determined using the determined weight and the brake cylinder pressure is controlled at the determined rate of change. The rate of change of brake cylinder pressure is determined so that the determined brake cylinder pressure is reached at a predetermined time for initiation for a given train brake command. The predetermined time is selected so that the determined brake cylinder pressure is reached substantial simultaneously on all cars on the train having an electropneumatic brake valve. Alternatively, the select time can be determined such that the determined brake cylinder pressure is reached at a time after initiation for a given train brake command that would be reached by the car if the car had a pneumatic brake control valve. This allows it to mimic a pneumatic brake control valve in a mixed train.
The braking efficiency of the car is determined and used in calculating the fixed brake ratio. The ratio is recalculated for changes in weight and for changes in determined brake efficiency.
The process further includes determining if a load responsive braking modification device is on the car and compensating the determined brake cylinder pressure for braking modification reduced by the modification device. Preferably, the type of load responsive brake modification device is determined so that the type of modification can be calculated.